JP2007-064131A, published by the Japan Patent Office, proposes fuel injection control implemented on a dual injection internal combustion engine having a port injector that injects fuel into an intake port and a direct injection injector that injects fuel directly into a combustion chamber. A dual injection internal combustion engine is applied to an internal combustion engine that requires a particularly high output such that a required amount of fuel cannot be supplied merely by injecting fuel into the combustion chamber through the direct injection injector.
In the fuel injection control according to the prior art, when a fuel cut condition is established in the internal combustion engine, fuel injection by the port injector is stopped first, whereupon fuel injection by the direct injection injector is stopped. The reason for this is as follows.
A part of the fuel injected into the intake port by the port injector adheres to a wall surface and so on of the port. The fuel adhered to the wall surface of the port takes a longer time to reach the combustion chamber than the fuel that flows into the combustion chamber without adhering to the wall surface of the port. When injection by the port injector and injection by the direct injection injector are stopped simultaneously upon establishment of the fuel cut condition, combustion by the internal combustion engine stops at that point. Since the fuel adhered to the wall surface and so on of the port reaches the combustion chamber at a delay, however, combustion may already have stopped at the point where this fuel reaches the combustion chamber. When the fuel that reaches the combustion chamber after combustion has stopped is discharged as unburned fuel, an exhaust gas composition inevitably deteriorates.
In the prior art, injection by the direct injection injector is continued for a fixed period following establishment of the fuel cut condition so that fuel combustion in the combustion chamber is maintained until the fuel adhered to the wall surface and so on of the port after being injected by the port injector reaches the combustion chamber at a delay. As a result, the fuel that reaches the combustion chamber at a delay is burned reliably.